In a long-range land-to-sea (LRLS) communication using variable-time-slot-TDMA (VTS-TDMA) in the 5 GHz unlicensed shared spectrum, which include a Base Transceiver Station (BTS) on land and Customer Premises Equipment (CPE) out in sea (on ships), communication end-points do not have any knowledge of interference at other end before connection is established. CPEs listen to broadcast Time Division Duplex (TDD) messages from a BTS on a given frequency and have the Signal to Noise Ratio (SNR) metric in a downlink. However, a BTS does not have a similar metric in an uplink before a connection is established to the CPE.
Further, interference is uncontrolled in unlicensed shared spectrum unlike in Long Term Evolution (LTE). Qualifying the interference before a network entry or a handover of the CPE is therefore important to sustain a connection and guarantee Service Level Agreement (SLA). Further, in selecting a potential BTS from a plurality of BTSs for the network entry or the handover, utilization of the BTS needs to be factored into a decision to maximize throughput for the CPE after connection establishment. This is critical in a Time Division Multiple Access (TDMA) system.
In the LRLS communication, when uplink interference is not evaluated and used in a decision metric to establish the network entry or the handover, there is an SLA maintenance issue at the CPE, if the throughput drops below 3 MBPS or the LRLS connection times out and link drops. Network communication in the uplink (TCP ACKs) will be limited by this interference, which will cause a throughput drop in the downlink or TDD timeouts in the uplink leading to link tear down. In such a scenario, there is a need to switch data-path to Very Small Aperture Terminal (VSAT) network to maintain the SLA. When channel conditions improve, data-path may switch back to LRLS network (from VSAT). This switching back and forth of data-paths, between LRLS and VSAT channels is likely to get into unnecessary “flapping” (ping-pong) effect. Such switching back and forth affects overall Quality of Experience (QoE). Since the LRLS operates in a shared spectrum, the channel quality becomes unpredictable based on usage of the shared spectrum by other entities. This may aggravate the flapping issue post switching of the channel from VSAT to LRLS under unfavorable conditions of the LRLS channel.
In some conventional systems, handovers are performed based on quality metrics such as signal strength or some measure of it or based on distance of a CPE from BTS. Also, in some conventional systems, for network entry, Automatic frequency selection (AFS) mechanism and link drop under interference are used. However, these conventional systems have the following limitations: handover decisions do not consider interference in the uplink and the downlink, distance of the CPE from a BTS is a hard to quantify metric in interference limited (5 GHz shared spectrum) TDMA based systems, AFS mechanisms do not guarantee SLA under interference, and no conclusive solution to mitigate ping-pong effect.